Ionization pressure gauge tube

ABSTRACT

An ionization pressure gauge tube is designed as a triode including an electron-emitting hot cathode, an electronaccelerating electrode and an ion collector arranged between the cathode and the accelerating electrode. The cathode, accelerating electrode and collector have dimensions and a relative arrangement such that the triode system has a transconductance of 0.25 to 1.00. The accelerating electrode is designed as a cylinder and the ion collector is designed as a system of 3 to 5 rods extending parallel to the axis of the tube and arranged symmetrically around the cathode. The cylindrical accelerating electrode has a diameter of from 8 to 16 mm.

United States Patent 11 1 Mennenga Sept. 18, 1973 [54] IONIZATION PRESSURE GAUGE TUBE 2,829,337 4/1958 Groendijk 324/33 2,497,213 2/1950 Downing 324/33 [751 Invent Herman" Mennenga Balms, 3,067,346 12/1962 Pennington 313 7 Germany [73] Assignee: Balzers Patent-Und Primary Examiner-Harold A. Dixon Beteiligungs-Aktiengesellschaft, Attorney-John J. McGlew et a1. Balzers, Liechtenstein [22] Filed: Oct. 26, 1971 [57] ABSTRACT [21] Appl- 192,633 An ionization pressure gauge tube is designed as a triode including an electron-emitting hot cathode, an 0 Foreign Application p i i D electron-accelerating electrode and an ion collector arranged between the cathode and the accelerating elec- Oct. 15, Sw1tzerland trode. The cathode, accelerating electrode and collec tor have dimensions and a relative arrangement such Related Apphcat'm' Data that the triode system has a transconductance of 0.25 Continuation of 366,504, 0% I5, 1969, to 1.00. The accelerating electrode is designed as a cylabandonedinder and the ion collector is designed as a system of 3 to 5 rods extending parallel to the axis of the tube and [52] US. Cl. 313/7, 250/83.6 R, 324/33 arranged symmetrically around the cathode The cylim [51] Int. Cl G0lt 1/18, G010 27/00 drical accelerating electrode has a diameter of from 8 [58] Field of Search 250/83.6 R; 324/33; to 16 mm 1' 2D in,Fiures [56] References Cited 4 C aims s 8 UNITED STATES PATENTS 3,353,048 11/1967 Hagenlocher 324/33 PATENTEDSW 3.760.212

G 2 INVENTOR.

HAWMANN MENNENGA Arm/mars BACKGROUND OF THE INVENTION Ionization pressure gauge tubes for low pressures below about Torr are in use in many designs. Those designed for higher pressures, however, have not been very successful to date, because of the disadvan tages connected with their operation. Particulars on these tubes and examples of construction of known ionization pressure gauge tubes for higher pressures may be found in:

THE REVIEW OF SCIENTIFIC INSTRUMENTS V0. 28, No. 12, December, 1967, pp. 1051 1054 (G. J. Schultz and A. V. Phelps: Ionization Gauges for Measuring Pressures up to the Millimeter Range) and PROCEEDINGS OF THE SUMPOSIUM ON ELEC- TRON AND VACUUM PHYSICS, Hungary 1962, Budapest 1963, pp. 403 411 (G. Hinzpeter; Use of Ionization Pressure Gauge Tubes in the Fine Vacuum Range).

Ionization pressure gauge tubes for higher pressures include an electron-emitting hot cathode, an electrode for the acceleration of the electrons emitted by the hot cathode, and an ion collector, whose function it is to collect the positive ions produced by the accelerated electrons in the gas space, according to the gas density (and thus the gas pressure). The ratio of the measured current of positive ions (1+) to the current of the electrons emitted by the cathode (I-) then constitutes, as is known, a measure of the quality of the vacuum in the measured space. In the linear measuring range there is applicable the equation I+/I- pS where p is the pressure to be measured and S is a proportionality constant (Sensitivity).

An ionization pressure gauge suitable for industrial practice should furnish a linear indication over the entire measurement range. The fraction of ions collected by the ion collector depends, however, on the mean free length of path of the electrons in the gas space, and therefore decreases with increasing pressure. A cause of this phenomenon is that, with increasing pressure, more and more ions are lost by recombination before they can reach the ion collector. This impairs the linearity of indication at higher pressures.

To preserve the linearity to the highest possiblepressures, it has been proposed to make the distances between the individual electrodes of the measuring system as small as possible. However, this requires a high precision of mechanical construction, and already slight deviations from the theoretical dimensions, as may easily occur when the electrode system is heated up for the purpose of degasing, result in great errors of measurement.

The use of a triode with an axially oriented hot cathode, a negative spiral grid as the ion collector and an anode coaxially surrounding this arrangement and accelerating the electrons, for the measurement of gas pressures, is known. In such a system, where the ioncollecting grid has a distance from the hot cathode of about 0.75 mm (l/32 inch) and the diameter of the anode cylinder is about 3 mm (/6 inch), a linear indication was obtained to about 1 Torr. To produce such an electrode system industrially with the narrow tolerances that are required for a gauge tube which is to be exchangeable in a measuring circuit means high expense. Moreover, the sensitivity of these known gauge tubes has been very low (10 Torr").

In other known arrangements, there have been used, as electronic accelerating and ion collecting-electrodes, plane-parallel plates at small spacings from each other and between which a hot cathode is installed. Such an arrangement also requires high precision in manufacture.

SUMMARY OF THE INVENTION This invention relates to the measurement of pressures in vacuum chambers and, more particularly, to the measurement of relatively high. pressures up to several Torr (Hg mm) with an improved ionization pressure gauge tube.

In contrast to the prior art, the problems solved by the present invention is that of vacuum measurement by means of triodes which, for a greater linearity range, permit using dimensions which are controlable without great expense during manufacture, and which, at the same time, attain a greater sensitivity.

In accordance with the invention, an ionization pressure gauge tube is designed as a triode, and comprises an electron-emitting hot cathode, an electronaccelerating electrode and an ion collector arranged between the hot cathode and the accelerating electrode. This ionization pressure gauge tube is characterized in that the arrangement of the three mentioned electrodes and their dimensions are selected in a manner such that the triode system has a transconductance of 0.25 to 1.0.

By transductance" D in the sense of this description, there is to be understood the ratio CAK/CGK of the electrostatic capacity C between the electronaccelerating electrode (anode) and the cathode, on the one hand, and the electrostatic capacity C between the ion collector and the cathode, on the other hand. This ratio may be expressed as D ur/C With the mentioned arrangement of the electrodes and the mensioned dimensions, there can be obtained a linearity range up to several Torr, despite the fact that the dimensions of the electrode system are much greater than has hitherto been considered necessary according to previous experience-The larger system dimensions permit greater tolerances in manufacture and result in greater stability in operation.

An object of the invention is to provide improved means for measuring pressures in vacuum chambers.

Another object of the invention is to provide an improved ionization pressure gauge tube for the measur' ing of relatively high pressures in vacuum chambers.

A further object of the invention is to provide such a tube which is designed as a triode and which, for a greater linearity range, permits the use of dimensions controllable without great expense to manufacture while at the same time attaining a higher sensitivity.

Another object of the invention is to provide such a tube which comprises an electron-emitting hot cathode, an electron-accelerating electrode and an ion collector arranged between the cathode and the accelerating electrode and which is characterized in that the arrangement of the electrodes and their dimensions are selected such that the triode system has a transconductance of 0.25 to 1.00.

A further object of the invention is to provide such an ionization pressure gauge tube in which the larger system dimensions permit greater tolerances in manufacture and result in greater stability in operation.

An understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a partially broken away perspective view illustrating the mechanical construction of the triode systems; and

FIG. 2 is a schematic wiring diagram of a simple measuring circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a hot cathode l is installed between two holding rods 2 and 3 which constitute, at the same time, heating current supply electrodes or conductors. Four electrically interconnected rods 4 are carried by a pipe 5 and conjointly form the ion collector. The electron-accelerating electrode is a cylinder 6 surrounding hot cathode l and rods 4. The rods 4 extend parallel to hot cathode l in symmetrically spaced relation from each other and from the hot cathode, and cylinder 6 is also coaxial with hot cathode 1. Cylinder 6 is connected with the external circuit through a holding rod 7. The inside diameter of cylinder 6 is 12 mm, and its length is 25 mm. The distance of rods 4 from cathode l is 4 mm, the diameter of hot cathode l is 0.5 mm, and the diameter of each rod 4 is substantially 0.5 mm.

The described electrode system is present in the space in which the gas pressure is to be measured, and can be used in a simple circuit illustrated in FIG. 2 which shows only the essential elements. Referring to FIG. 2, the indirectly heated hot cathode 1, whose heating circuit has not been illustrated, is connected to ground potential through a measuring instrument 11 for measuring the emission current I-. Ion collector 4 has applied thereto a negative potential of, for example, --50 V, and the electron-accelerating electrode 6 has applied thereto a positive potential of about lOOOV relative to ground. A measuring instrument 12 is provided to measure the ion current.

With the mentioned dimensions of the triode system, a sensitivity of 1.7 Torr", or more than 100 times the sensitivity of the known triodes mentioned above, has been attained. The indication for nitrogen, at an emission current of 7 microamperes was linear from to 1 Torr. This high sensitivity in the small area of the ion collector provide, as compared with known designs of pressure gauge tubes for higher pressures, a much lower so-called roentgen limit. For the illustrated example, this limit is below 10 Torr. Thus, the ionization pressure gauge tube of the invention can cover a measurement range for which, previously, two different tubes were required.

Besides the circuit described with reference to FIG. 2, there may be used also other known circuits for ionization pressure gauge tubes of analogous design as used for lower pressures, having, for example, special devices for the stabilization of the electron emission current.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise, without departing from such principles.

What is claimed is:

1. An ionization pressure gauge tube, designed as a triode and capable of measuring pressures less than one Torr and of measuring pressures up to several Torr with an increased sensitivity and linearity, said tube comprising, in combination, a substantially rectilinear electron-emitting hot cathode; conductor means fixedly supporting opposite ends of said hot cathode; an electron-accelerating electrode in the form of a cylindrical electrically conductive metal shell having a substantially imperforate side wall and an axial length of the order of the length of said hot cathode; said hot cathode extending coaxially of said cylindrical shell; and an ion collector arranged between said hot cathode and said electron-accelerating electrode and spaced from said cathode and said accelerating electrode; said ion collector comprising a system of three to five rectilinear rods extending outwardly from spaced points in a common support and in spaced parallel relation to said cathode; said rods being free of mechanical connection to each other except through said common support and having free and spaced outer ends; said rods being arranged at equal radial distances from said cathode and at equal angular spacings from each other; said cathode, said electrode and said collector having dimensions and a relative arrangement providing the triode system with a transconductance of 0.25 to 1.0.

2. An ionization pressure gauge tube, as claimed in claim 1, in which there are four of said rods constituting said ion collector.

3. An ionization pressure gauge tube, as claimed in claim 1, in which said electron-accelerating electrode has a diameter of from 8 to 16 mm.

4. An ionization pressure gauge tube, as claimed in claim 2, in which the diameter of said cathode is of the order of 0.5 mm, the diameter of said rods is of the order of 0.5 mm, and the spacing of said rods from said cathode is of the order of 4 mm.

I I I 

1. An ionization pressure gauge tube, designed as a triode and capable of measuring pressures less than one Torr and of measuring pressures up to several Torr with an increased sensitivity and linearity, said tube comprising, in combination, a substantially rectilinear electron-emitting hot cathode; conductor means fixedly supporting opposite ends of said hot cathode; an electron-accelerating electrode in the form of a cyliNdrical electrically conductive metal shell having a substantially imperforate side wall and an axial length of the order of the length of said hot cathode; said hot cathode extending coaxially of said cylindrical shell; and an ion collector arranged between said hot cathode and said electronaccelerating electrode and spaced from said cathode and said accelerating electrode; said ion collector comprising a system of three to five rectilinear rods extending outwardly from spaced points in a common support and in spaced parallel relation to said cathode; said rods being free of mechanical connection to each other except through said common support and having free and spaced outer ends; said rods being arranged at equal radial distances from said cathode and at equal angular spacings from each other; said cathode, said electrode and said collector having dimensions and a relative arrangement providing the triode system with a transconductance of 0.25 to 1.0.
 2. An ionization pressure gauge tube, as claimed in claim 1, in which there are four of said rods constituting said ion collector.
 3. An ionization pressure gauge tube, as claimed in claim 1, in which said electron-accelerating electrode has a diameter of from 8 to 16 mm.
 4. An ionization pressure gauge tube, as claimed in claim 2, in which the diameter of said cathode is of the order of 0.5 mm, the diameter of said rods is of the order of 0.5 mm, and the spacing of said rods from said cathode is of the order of 4 mm. 